1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and more particularly to color conversion for reproducing colors represented by combinations of RGB signals or the like with combinations of signals of color materials such as ink.
2. Description of the Related Art
As an example of this type of color conversion, Japanese Patent No. 4003046 shows a color conversion table that defines combinations of inks used to reproduce colors on a gray axis (FIG. 7 of Japanese Patent No. 4003046). More specifically, the color conversion is performed such that a black pixel (R=G=B=0) having a gray level (gradation value) of 0% is printed with only black (K) ink and color pixels having gray levels higher than the gray level of 0% are printed with black ink and color inks such as cyan (C) and magenta (M). Such color conversion allows not only printing with improved image quality such as gray balance but also achieving desired print conditions by reducing banding, for example.
However, in a case where the above-described color conversion is performed on image data that is compressed and decompressed with a lossy compression method, as a result of printing based on a combination of color material signals obtained by the color conversion, colors different from the expected colors of the image data before compression may be reproduced.
For example, when image data representing black (R, G, B)=(0, 0, 0) such as black character is compressed and decompressed with a lossy compression method, the resulting image data may have a signal value different from (R, G, B)=(0, 0, 0). Meanwhile, in the color conversion as described above, there is a case where black of a signal value of (R, G, B)=(0, 0, 0) is printed only with black ink, while a color of a signal value other than (R, G, B)=(0, 0, 0) is printed with black ink and color inks. In this case, after being compressed and decompressed, the original black of image data will be printed not only with black ink but also with color inks. As a result, density of the black image such as black character, for example, falls below a desired density, thereby decreasing print quality.